Question: how to properly convert between LocalDateTime (or LocalDate/LocalTime with what's available) and Date/Calendar?

[jakewharton]

Question: how to properly convert between LocalDateTime (or LocalDate/LocalTime with what's available) and Date/Calendar?

[AndroidDeveloperLB]

ok, so I've made some nice helper functions, for all conversions:

Date<->LocalDate

fun Date.toLocalDate(): LocalDate = LocalDate.of(year + 1900, month + 1, date)
fun LocalDate.toDate(): Date = Date(year - 1900, monthValue - 1, dayOfMonth)

Calendar<->LocalDate

fun Calendar.resetTimeFields(): Calendar {
    set(Calendar.HOUR_OF_DAY, 0)
    set(Calendar.SECOND, 0)
    set(Calendar.MINUTE, 0)
    set(Calendar.MILLISECOND, 0)
    return this
}

fun Calendar.toLocalDate(): LocalDate = LocalDate.of(get(Calendar.YEAR), get(Calendar.MONTH) + 1, get(Calendar.DAY_OF_MONTH))

fun LocalDate.toCalendar(): Calendar {
    val cal = Calendar.getInstance().resetTimeFields()
    cal.timeZone
    cal.set(year, monthValue - 1, dayOfMonth)
    return cal
}

epochTimeInSeconds<->LocalDate

    @JvmStatic
    fun getFromEpochSecond(epochSecond: Long): LocalDate = Instant.ofEpochSecond(epochSecond).atZone(ZoneId.ofOffset("UTC", ZoneOffset.ofHours(0))).toLocalDate()

fun LocalDate.toEpochSecond(): Long = atStartOfDay(ZoneId.ofOffset("UTC", ZoneOffset.ofHours(0))).toEpochSecond()

Just thought it might be useful...

[AndroidDeveloperLB]

In Kotlin, I've made these extension functions for Calendar<->LocalDate :

fun Calendar.toLocalDate(): LocalDate = LocalDate.of(get(Calendar.YEAR), get(Calendar.MONTH) + 1, get(Calendar.DAY_OF_MONTH))

fun LocalDate.toCalendar(): Calendar {
    val cal = Calendar.getInstance().resetTimeFields()
    cal.set(year, monthValue - 1, dayOfMonth)
    return cal
}

Are those correct?

[JakeWharton]

Usage questions for ThreeTenBP can be asked on StackOverflow. This library is just a repackaging of the timezone database.